The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Shock absorbers are used in conjunction with automobile suspension systems and other vehicle suspension systems to absorb unwanted vibrations which occur during operation of the vehicle. To absorb this unwanted vibration, shock absorbers are connected between the sprung mass (the body) and the unsprung mass (the suspension system) of the vehicle. A piston is located within a pressure tube of the shock absorber and is connected to the sprung mass of the vehicle. The pressure tube is connected to the unsprung mass of the vehicle and is normally filled with hydraulic fluid. Because the piston has the capability to limit the flow of hydraulic fluid within the pressure tube when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the suspension (unsprung mass) to the body (sprung mass) of the vehicle.
A conventional mono tube shock absorber comprises a pressure tube with a piston disposed therein. A piston rod is connected to the piston and it extends through the upper end of the pressure tube. The damping forces are created by the restricted flow of fluid through fluid passages and valving in the piston which regulates passage of fluid between opposite sides of the piston within the working chamber.
Due to the piston rod being located on only one side of the piston, a larger amount of fluid is displaced in the lower working chamber than the fluid that is displaced in the upper working chamber. The difference in the amount of fluid is termed the rod volume and this difference is typically accommodated for by an additional piston in the working chamber that separates the fluid in the working chamber from a gas chamber usually disposed below the additional piston.
A conventional dual tube shock absorber comprises a pressure tube with a piston disposed therein and a reserve tube surrounding the pressure tube. A piston rod is connected to the piston and it extends through the upper end of the pressure and reserve tubes. At the lower end of the pressure tube, a base valve is located between the pressure tube and the reserve tube. The base valve controls fluid flow between the working chamber defined by the pressure tube and the reserve chamber defined by the reserve tube. The damping force is created by the restricted flow of fluid through passages and valving in the piston which regulate passage of fluid between opposite sides of the piston within the working chamber and by the restricted flow of fluid through passages and valving in the base valve which regulate passage of fluid between opposite sides of the base valve between the working chamber and the reserve chamber.
Due to the piston rod being located on only one side of the piston, a different amount of fluid is displaced on the compression stroke as opposed to the rebound stroke. The difference in the amount of fluid is termed the rod volume. The rod volume of fluid is pushed out of the pressure tube, through the base valve and into the reserve tube during a compression stroke. During a rebound stroke, the rod volume of fluid flows in the opposite direction from the reserve tube, through the base valve and into the pressure tube.
The piston rod is supported at its lower end by the piston and is slidingly received at the upper end of the shock absorber by a rod guide. The piston rod guide thus functions as a slide bearing for the piston rod. The rod guide properly positions the piston rod within the pressure tube and also acts as a closure member for both the pressure tube and the reserve tube. In order for the smooth sliding of the piston rod through the rod guide, a slight clearance is formed between the inner periphery of the bearing portion of the rod guide and the outer periphery of the piston rod. This slight clearance allows for the hydraulic fluid to lubricate the interface between the piston rod and the rod guide.
Shock absorbers typically include a dirt shield which is a metal skirt which is attached to an upper portion of the piston rod and extends down over the pressure tube in a mono-tube design and down over the reserve tube in a dual-tube shock absorber when the shock absorber is in a compressed condition. When the shock absorber extends in length, the dirt shield travels with the piston rod to cover the exposed portion of the piston rod. The covering of the exposed portion of the piston rod helps to prevent dirt and other contaminants from contacting and possibly sticking to the piston rod. This dirt and other contaminants could cause damage to the sealing system of the shock absorber during a subsequent compression stroke of the shock absorber.
Typical piston rods are a two-piece welded assemblies where the upper stem or attachment loop is resistance or friction welded to the lower portion of the shock absorber. When a dirt shield is included, it is welded at the same time and in the same position as the resistance or friction weld. This provides for the welding of the three components in one weld operation.
In a number of higher load applications, this single weld operation welded component cannot meet the durability requirements in relation to static and dynamic loads due to the disturbed area at the weld. In order to improve the durability and the resistance to these higher static and dynamic loads, the typical solution is to add a first metal inert gas (MIG) weld or a first metal active gas (MAG) weld between the dirt shield and the upper stem or attachment loop and a second MIG weld or a second MAG weld between the dirt shield and the lower portion of the piston rod. This increases the single-weld operation to a three-weld operation.